AT&T just released its quarterly numbers, and the company’s smartphone sales are still completely dominated by the iPhone. The company activated 3.7 million iPhones for the quarter, which represents 73 percent of all the smartphones sold (if each is taken as a new iPhone sold – there is likely a negligible difference). Additionally, 22 percent of the new iPhones sold were to new AT&T customers.

Strong Smartphone Sales Continue. AT&T sold 5.1 million smartphones in the second quarter. Smartphones represented 77 percent of postpaid device sales. At the end of the quarter, 61.9 percent, or 43.1 million, of AT&T’s postpaid subscribers had smartphones, up from 49.9 percent, or 34.1 million, a year earlier. AT&T’s ARPU for smartphones is twice that of non-smartphone subscribers, and about 88 percent of smartphone subscribers are on FamilyTalk® or business plans. Churn levels for these subscribers are significantly lower than for other postpaid subscribers. More than one-third of AT&T’s postpaid smartphone customers use a 4G-capable device.

Android, iPhone and Windows device sales were supported by AT&T’s 4G network. Only AT&T’s 4G network lets iPhone 4S download three-times faster than any other U.S. carrier’s network. In the quarter, the company activated 3.7 million iPhones, with 22 percent new to AT&T.

The percentage would represent a slight downturn for AT&T over last quarter, where iPhone represented around 78 percent of smartphone activations with 4.3 million cumulative. The number is also up slightly over the year ago. AT&T activated 3.6 million iPhones in Q2 2011. Note: Sprint did not sell iPhones at the time.

Perhaps most interestingly, with AT&T’s Smartphone numbers at 77% and iPhones representing 73% of that, iPhones, over a half year after launch, still represent over 55% of AT&T’s total Phone sales. AT&T is truly dependent on Apple.

We will cover Apple’s quarterly announcement later today, where we will get total device numbers across Apple’s line of products.